[Mailman-Users] Confirmation by reply not working

[Keith Seyffarth]

Hello,

I'm having problems with the confirmation by reply working. When a user
is invited to the list, or when a user subscribes on the web for, or
when a user subscribes by emailing -join@, they are sent the
confirmation email.

If they replay to the email or create a new message and send ONLY the
confirmation code as instructed, nothing happens. However, if they try
again with the same confirmation code, they will get a response back
that the confirmation code is no loger valid. This appears to indicate
that mailman is receiving the email and processing it, but not actually
subscribing them to the list.

This is happening after moving to CentOS 7 using PLESK 12.5...

Any ideas on what could be going on?